Real-time model-based feedback is something that is far from commonplace in today's world. The basic concept of real-time feedback is to take a physical system, modeled by mathematic equations, and then couple it with a computer as a virtual system.

Sensor monitoring gives the processing logic an idea of how well the real world system is conforming to the theoretical model. The results are processed and yield adjustments (feedback) to the real world system to make it in tune with the theoretical model. The result is that the virtual and real world models converge into a single "mixed reality" system, bridging a the virtual (theoretical) and physical world.

Researchers at the University of Illinois created a virtual pendulum and a real world counterpart that behaves as the world's first mixed reality system. Bidirectional instantaneous coupling, adjustments both to the real world pendulum by motor feedback and the virtual pendulum by tweaking mathematical parameters, yielded a single system in which both systems' are synchronized. The result is two pendulums swinging as one.

The experiment, the first fully successful one of its kind, sounds simple but raises mind-blowing questions about reality. According to Illinois physicist Alfred Hubler, "In a mixed reality state there is no clear boundary between the real system and the virtual system. The line blurs between what’s real and what isn’t."

Two physical mechanical systems have been previously coupled, but never before has a real world and virtual one been mixed. Such a breakthrough was only possible thanks to ultra-fast computing, which allowed real-time processing of the pendulum data, and real-time response. Hubler states, "Computers are now fast enough that we can detect the position of the
real pendulum, compute the dynamics of the virtual pendulum, and
compute appropriate feedback to the real pendulum, all in real time."

Hubler thinks that eventually coupling of the real and virtual worlds, may lead to it being hard to tell what is real and what is fake -- a topic immortalized by generations of science fiction writers. Hubler worries people may become defensive and paranoid in the real world, based on threats in the virtual world.

The research was funded by the National Science Foundation and will be presented by Hubler at the annual American Physical Society meeting, which will be held in New Orleans, March 10-14, 2008.

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